Process for impregnating carbon brushes



L. E. MOBERLY 2,418,420

PROCESS FOR IMPREGNATING CARBON BRUSHES Filed Feb. 8, 1943 April 1, 1947.

INVENTOR WlTNESSES:' um Lawrince Moberl}.

Patented Apr. 1, 1947 UNITED STATES PATENT OFFICE PROCESS FOR IMPREGNATIN G CARBON BRUSHES Lawrence E. Moberly, Wilkinsburg, ,Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 8, 1943,. Serial No. 475,182

7 Claims.

conditions corresponding to a.40,000-fot altitude and a moisture content corresponding to a dew point, of 50. C. Under such conditions, ordinary carbon brushes will wear and dust at a rapid rate, and the brush-es can not be used for prolonged periods, of time. This has been discovered to occur at high altitudes in electrical motors and generators employed on aircraft.

It was disclosed in the aforementioned patent application that halogen compounds, particularly .halide salts of metals exemplified by lead iodide,

cadmium. iodide, silver iodide, cadmium chloride,

potassium fluoride and cadmium bromide, .when

.applied to the brushes either by impregnation .or. other mode, of distribution therein, will cooperate with the commutator or other current collector to reduce the wear and dusting in atmospheric conditions corresponding to those generally experienced at high altitudes.

,In applying halide salts of metals to carbon electrodes, such as electrographitic brushes, in order to reduce excessive wear and dusting under -high altitude conditions, ithas been discovered that about 40% or moreby weight of the me- .tallic halide salt based on the weight of the brush isrequired for best results. --,salt cannot readily be introduced into the highly .compacted, finely porous, carbo-naceous material in the brushes by conventional methods. Soak- This amount ofsuch ing the brush in saturated aqueous solutions of ,most metallic ,chlorides, iodides, fluorides. and ,bromides, for instance, does not always provide for introducing a sufiiclent amount of the salt to give the optimum results since some of the salts, such for example, as lead iodide, are only slightly soluble in water.

Immersing brushes in the molten halide salt compound also has been found to berelatively unsatisfactory. The fine porosityof the brushes, *in combination with the gases normally present in the .pores, appears to greatly ,restrainpenetra- ..tion of'the-imolten compound. In some cases, "one hour immersion has been barely, satisfactory fto eivez an adequateamount of melted salt pene- .tration and deposition in the pores of the brushes.

Whenit is considered that carbon brushesnumbering millions must betreated with a predetermined .amount of salt, sucha process is .notentirely practical.

The object of the inventionis to providea method of impregnating carbon brushes with metallic halide salts.

Other obejcts of the invention will, in part, the obvious, and will, in, part, appear hereinafter.

.For a fuller understanding of the nature, and

, objects of this invention, referenceshould be, had

to the figures of thedrawingyvhere:

Figure 1, partly in section, shows aschematic arrangementfor carrying out the processof this invention; and

Fig. 2 is aviewin elevation of abrush with halide saltdeposited thereon.

According to this invention, it hasbeen dis- .covered that halide salts may be rapidly and ef- -,fi iently a i d in re et m ne a un ,1 bq brushe m rl h a t directly 90 thebrushes to produce electrodes having low wear and dusting characteristics when operating under .high altitude conditions.

For an example of the invention, reference should be had to thefigure of the drawing in which there is illustrated a schematic arrangement of a brush impregnating apparatus ID." At

the left handof the apparatus, individual brushes H2, or carbon plates from which a number of brushes may be made, to be treated are placed on an endless conveyor It disposed for operation about pulleys l6 and i8 operated from a suitable source of powerata predetermined rate of, travel. A receptacle, 20, filled Withthe dry crystalline or w e ha iq sa t such. or xamp as te iodide, ;is disposedabove thebrushes l2 on conveyor M. A measuring wheel-22 having pockets of a predetermined, size is fed with the leadiodide from the container 20 whereby a, predetermined amount of the salt .is measured out in each pocket.

-A mechanism (not shown) actuated by the passage of thebrushes below the container. may be employed to turn themeasuring device 22 in synchronism therewith whereby a pocket is filled for each brush. The measured quantity of salt is emptied from the pockets and is distributed by the spout 24 upon eachbrush |2 as the brush passes therebelow on conveyor I4. Thus, each brush l2 has appliedto the upper surface thereof a .ineasuredlheap or ,layer 26 ,of the leadiodide.

Instead. of;.a-, powder,, ,preformed tablets of a predetermined weight of metal halide may be 3 applied by a similar device to each carbon brush or plate on the conveyor.

The conveyor l4 carries the brushes with the predetermined amount of salt applied thereto into the furnace or oven 28 which is heated from a suitable source of energy to maintain a temperature well above the melting point of the salt. In the case of lead iodide, the temperature of the furnace will be about 500 0. As the brushes enter the furnace 28, the salt 26 on each brush is heated to the melting point and the molten salt rapidly penetrates the brush to thoroughly impregnate the pores thereof. For some reason not entirely known, the impregnation of the brush occurs at a rate many times greater than when the same brush is immersed in a bath'of the molten compound. The high'rate of penetration is entirely unexpected. Less than ten minutes in the furnace 28 is sufficient for the complete absorption of the molten compound in a carbon body of the size of 1 inch by /2 inch by /4 inch.

The heat treated salt impregnated brush is carried out of the oven on the conveyor 14 where it cools rapidly and may be put in use at once. To prevent an untoward reaction of the atmosphere with the hot salt, it may be desirable to effect cooling in a nonoxidizing atmosphere maintained in a separate cooling chamber at the end of the conveyor.

In order to retain the fluid molten halide salt in contact with the upper surface of the carbon bodies during impregnation, any suitable method well known to those skilled in the art may be employed. One method that has been found to be satisfactory has been to provide a ledge or dam around the body as shown in Fig. 2. The carbon body l2 may be channeled to produce a pocket ll defined by the ledges l3 at the sides at the upper surface. Large flat plates of carbon can be prepared, by molding or machining, with a pocket H in the center to provide a continuous ledge about all the edges. Smaller plates can be channeled and butted tightly against one'another while on the conveyor to form a continuous trough. A layer of pitch, tar, resin, or other suitable cement can be applied between adjacent bodies to prevent molten salt leakage. The applied salt even when molten is thereby prevented from running off since it is retained in a pocket II. In some cases separate members may be applied about the sides of carbon plates l2 to dam in the melted salt.

In order to secure a uniform distribution of metallic halide salt over the entire area of a plate l2 such as is shown in Fig. 2, the halide 26 should be evenly applied over the entire pocket II. It has been found that upon reaching the melting point the metallic halide generally penetrates only the portions of the brush directly below it without spreading laterally to an great extent. Thus, if the heap 25 of powdered halide is applied over only a limited surface area, nonuniform impregnation may result and some brushes cut from plate l2 may contain but little impregnant.

A different method of applying an even layer of metal halide over the surface of pocket II is to mix the metal halide, such as lead iodide, with an easily volatilized binder such as polystyrene, coumarone-indene resins, or the like and extrude the mixture as a thin ribbon as wide as pocket II. The thickness of the ribbon should be suffi cient to distribute in each, unit volume of carbon in the plate l2 therebelow a predetermined quantity of lead iodide. The extruded ribbon is placedin pocket I I and upon heating, the easily volatilized binder evaporates before the lead iodide melts. For instance, polystyrene will depolymerize and the monomeric styrene will evaporate at temperatures of about 300 C. Thereafter the lead iodide left as a residue may be melted by heating to about 500 C.

The furnace atmosphere may be made neutral in order to prevent excessive oxidation of the brush or inadvertent oxidation or decomposition of the lead iodide or other halide compound. A gas secured by burning natural gas in air to a predetermined extent and characterized by substantially neutral properties is one type of atmosphere suitable for the purpose of this invention; Other atmospheres, for example, an all nitrogen atmosphere, may be introduced into the furnace 28 for the same purpose.

Since the carbon plates I2 are relatively thin, the process may be made more eflicient by superimposing two or three or more plates with halide salt applied on the conveyor 14 for simultaneous treatment; The ledges l3 will provide for theproper spacing between each layer of plates. Separate spacers may be employed in case plates without ledges are being processed.

Measured amounts of halide salts may be applied manually or in other ways thanshown in Fig. 1. Likewise, carbon plates with the salt ap.. plied to the upper surface thereof may be manually placed in an oven and removed when fully impregnated. It will be clear to those skilled in the art that other forms of apparatus may be employed to carry out the process disclosed. For instance, the plates may be pushed along a graph ite trough into the furnace instead of being carried on the belt type conveyor shown in Fig. '1.

In some cases, instead of applying the salt in crystal form, the salt may be premelted and applied in a liquid state to the surface of the carbon plates previous to placing the plates in a furnace.

Other methods of depositing or applying the salt than by the measuring device to the brushes prior to the heat treatment have been found to be satisfactory. In some cases, a predetermined quantity of the salt made into a paste by adding a liquid thereto may be spread or brushed upon the upper surface of the brush and on entering the furnace the solvent or liquid carrier will be evaporated, leaving the dry salt in condition for melting and penetration of the carbon brush. The salt may be applied in any desirable physical state, since, when subjected to the high temperatures in the furnace, the salt will melt and impregnate the carbon body. V r

By applying a measured quantity of the salt to each individual brush, it will be apparent that there will be no question of whether or not each brush member has been given asatisfactory quantity of the iodide or bromide. Since it is quite important that each brush operate at the optimum efiiciency, it is desirable-that each brush have a minimum predetermined. quantity of salt present therein. i A may be treated ee- Any type carbon electrode cording to this invention, including graphitic brushes and metallic-carbon brushes. In practicing theprocess it has been found that graphitized brushes may be treated somewhat more satisfactorily than ungraphitized carbon. The graphitizing of carbon plates is believed to result in a greater porosity leading to a more rapid penetration and absorption of the salt.: By com- 7 parison metallic-carbon brushes have been found to absorb the amounts.

Since certain changes may be made in the above invention, and different embodiments of the invention may be made Without departing from the scope thereof, it is intended that all matter contained in the above disclosure or taken in connection with the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. The process of impregnating a graphitized carbon brush with a metallic halide comprising applying a predetermined amount of the metallic halide to an upper surface of the brush and heattreating the brush and applied solid halide to a temperature to melt the halide for a period of time sufiicient to cause the molten halide to penetrate into or be absorbed by the brush thereby securing a distribution of the metallic halide in the body of the brush.

2. The process of impregnating a carbon brush with a material capable of decreasing dusting and wear comprising applying a predetermined amount of a solid metallic halide material to a substantially horizontally disposed upper surface of the brush, and heating the brush and applied material to a temperature suificient to melt the material and to cause the molten metallic halide material to penetrate into or be absorbed by the brush to provide for a predetermined distribution of the material throughout the brush.

3. The process of impregnating a carbon brush with a metallic halide, comprising forming a pocket in an upper surface of a porous carbon body to be used in preparing the brush, applying a predetermined amount of the metallic halide in the pocket in the body and heating the body and applied metallic halide to temperatures sumcient to melt the halide, the pocket serving to retain the molten halide, the heat treatment being for a period of time sufiicient to cause the molten halide to penetrate the body and be absorbed thereby.

4. The process of impregnating carbon bodies with a metal halide comprising, in combination, mixing the metal halide with a binder which will evaporate below the melting temperature of the metal halide, forming the mixture into a ribbon having a predetermined weight of metal halide per unit area, applying the ribbon over a surface of the carbon body, and heating the ribbon to a temperature to cause the binder to evaporate and thereafter heating to a temperature to melt the salt very slowly and in lesser metal halide and to impregnate the carbon body.

5. In the process of incorporating a metallic halide in a porous carbon body, the steps comprising, disposing the porous carbon body in such position that an upper surface is substantially horizontal, applying to the substantially horizontal upper surface a predetermined amount of a solid metallic halide and heating the carbon body and applied metallic halide to a temperature high enough to melt the metallic halide.

6. In the process of incorporating in a porous carbon plate having substantially fiat surfaces a metallic halide, the steps comprising, disposing a substantially fiat upper surface of the carbon plate in a substantially horizontal plane, applying to the substantially flat upper surface a predetermined amount of solid metallic halide distributed relatively uniformly over the surface, heating the carbon body and applied metallic halide to a temperature high enough to melt the metallic halide, and continuing the heating until the molten metallic halide has penetrated into the pores of the carbon body and is distributed throughout the carbon body.

7. In the process of impregnating a carbon brush with a metallic halide salt, the steps of applying a quantity of the metallic salt to an upper surface only of the brush and heat-treating the brush and applied salt at a temperature at which the metallic salt will be molten and for a suificient time so that it will penetrate the brush to pro vide for a predetermined distribution of the metallic salt in the brush.

LAWRENCE E. MOBERLY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,000,761 Snyder Aug. 15, 1911 1,184,135 Rudolph May 23, 1916 1,626,104 Swift Apr. 26, 1927 1,716,461 Portail June 11, 1929 1,779,242 Laube Oct. 21, 1930 1,861,415 Hunter May 31, 1932 1,867,524 Orne July 12, 1932 1,868,206 Hunter July 19, 1932 1,895,756 Fuller Jan. 31, 1933 1,620,940 Bleecker Mar. 15, 1927 1,742,259 Kelleher Jan. 7, 1930 2,098,062 Palmer Nov. 2, 1937 

